1. Field of the Invention
The present invention relates to a disk cartridge which accommodates, in the interior thereof, and protects a disk medium for recording of information.
2. Description of the Related Art
Conventionally, in 3.5-inch flexible disks (FDs), mini-disks (MDs) and the like, a disc-shaped disk medium is accommodated within a case. At the time of reading or recording information from or onto the disk medium, a recording member or a reading member of a drive device accesses the disk medium from an opening portion of the case. Further, a shutter member which opens and closes the opening portion is provided at the case. In the usual state, the shutter member is at a closed position and closes the opening portion. As needed, the shutter member is moved by (a shutter opening/closing mechanism of) the drive device to reach an open position, and the opening portion is opened.
At the case accommodating the disk medium, the two case members are combined such that an accommodating portion for a disk medium is formed therebetween. Because the two case members have respectively different configurations, the number of parts increases and the parts costs increase.
In order to prevent the opening portion from being opened needlessly, it is preferable to provide, at the case, a lock member for locking the shutter member, an urging member for urging the shutter member to the closed position, and the like. However, by providing such members, the number of parts increases, which leads to an increase in the costs for parts.
Moreover, because the number of work processes for assembling parts increases due to the increase in the number of parts, the assembly costs also increase. In addition, in recent years, it has become desirable to make disk media smaller sized. When, in accordance with this trend, the respective parts are also to be made small-sized, the assembly work becomes even more difficult.
The configuration of the cartridge case of the disk cartridge along the planar direction (the planar configuration) is substantially rectangular. On the other hand, the width of the opening of a disk cartridge loading portion of a disk drive device is slightly wider than the dimensions of the short sides of the cartridge case, and is narrower than the long sides of the cartridge case. In this way, when loading the disk cartridge into the drive device, it is possible to prevent the cartridge case from being inserted into the loading portion of the drive device in a state of being rotated 90xc2x0 with respect to the correct direction of insertion, i.e., in the direction in which a long side of the cartridge case is inserted first.
However, when a user inserts the cartridge case into the loading portion of the drive device in a state of having rotated the cartridge case by 180xc2x0 with respect to the correct direction of insertion, it is possible, from a dimensional standpoint, to insert the cartridge case into the loading portion of the drive device. Accordingly, in order to prevent such incorrect insertion of the disk cartridge, a detecting means must be provided at the drive device in order to detect a cartridge case which has been incorrectly inserted into the loading portion in a state of having been rotated by 180xc2x0 with respect to the correct insertion direction. Such a means for detecting incorrect insertion may be, for example, a means which detects the insertion direction of the cartridge case by using an optical sensor or a magnetic sensor or the like. However, if such a means for detecting incorrect insertion is provided at the drive device, the structure of the drive device becomes complex, the number of parts increases and the cost of the device increases.
There are shutter opening/closing mechanisms of the above-described drive devices which, for example, open or close a shutter member by making a shutter opening/closing lever, which is formed in a pin-shape or a plate-shape, engage with the shutter member, and by moving the shutter opening/closing lever along the opening/closing direction of the shutter member.
In recent years, the development of small-sized disk cartridges and drive devices therefor has advanced as such small-sized disk cartridges and drive devices are utilized in mobile devices such as cellular phones and the like. As disk cartridges and drive devices have become more compact, of course, the shutter member at the disk cartridge and the shutter opening/closing lever at the drive device have also been made smaller. Such shutter members and shutter opening/closing levers have less relative dimensional accuracy and strength than shutter members and shutter opening/closing levers used in larger disk cartridges and drive devices. With such smaller structures, at the time of loading the disk cartridge into the drive device, it is difficult for the shutter opening/closing member to reliably be made to engage the shutter member.
Moreover, in a small-sized disk cartridge in which information can be recorded on and read out (played back from) both the obverse and reverse surfaces of the recording disk, usually, a window portion is formed in each of the obverse and reverse surfaces of the cartridge case, and a shutter member, for opening and closing the window portion, is disposed at each of the obverse side and the reverse side of the cartridge case. Accordingly, the configurations and dimensions of the shutter opening/closing lever and the shutter members are limited in order to, at the time of opening one shutter member by the shutter opening/closing lever, prevent the shutter opening/closing lever and the one shutter member from interfering with the other shutter member. When such limitations exist, it is extremely difficult to make the shutter opening/closing lever reliably engage with the shutter member when the disk cartridge is loaded into the drive device.
When a case, in which a disk medium is accommodated, is inserted into a drive device, the case is positioned within the drive device. Generally, a pair of reference holes for positioning are formed in the case along a direction orthogonal to the direction of insertion into the drive device, and positioning pins of the drive device can be fit into the reference holes.
Here, one reference hole is a completely circular portion, and the other reference hole is a flat oval portion. In this way, reference positioning of the case and the drive device is first carried out by the completely circular portion, and the flat oval portion absorbs the positional offset between the case and the drive device and the positional offset between the completely circular portion and the positioning pin when the case is tilted at the time of being loaded or discharged. In this way, galling between the positioning pin and the completely circular portion is mitigated.
When recording and playback are possible at both surfaces of the disk medium, there are cases in which the case is turned upside-down and inserted into the drive device. At such a time, the positions of the completely circular portion and the flat oval portion are reversed with respect to the positioning pins.
Thus, as shown in FIG. 18A, completely circular portions 500 and flat oval portions 502 are disposed so as to oppose one another. The completely circular portion 500 is disposed at a reference positioning pin 510 provided at a drive device (not shown), regardless of whether a case 504 (formed by a shell 506 and a shell 508) is upside-down or not.
However, as the case 504 is made to be ultra-compact, the case 504 is also made to be thinner. As shown in FIG. 18B, there are cases in which the distal end portions of the reference positioning pin 510 and a positioning pin 512 project from the shell 508 which is disposed at the lower side and reach the shell 506 disposed at the upper side.
In this case, the positional offset and the like between the completely circular portion 500 and the reference positioning pin 510 is absorbed at the positioning pin 512. Thus, regardless of the fact that the positioning pin 512 corresponds to the flat oval portion 502, the distal end portion of the positioning pin 512 fits together with the completely circular portion 500 of the shell 506, and there is the concern that problems will arise in the operations of loading and discharging the case 504.
Further, the case accommodating the disk medium is formed by fixing two shells (two case members) together by ultrasonic welding or the like.
A lock member which locks a shutter member in order to prevent inadvertent opening of the disk opening portion, an urging member which urges the shutter member toward its closed position, and the like are accommodated in the case. When the shells have been fixed together by ultrasonic welding, if the disk cartridge is deemed defective in a quality inspection, the parts thereof which could be used cannot be reused.
Thus, it is preferable to carry out ultrasonic welding after the disk cartridge has undergone a quality inspection. However, up until the time that the ultrasonic welding is carried out, the shells must be maintained in a temporarily fastened state so as to not come apart from one another.
In view of the aforementioned, an object of the present invention is to provide a disk cartridge which, by having a small number of parts, results in lower manufacturing costs and easy assembly, and in particular, to provide a disk cartridge which can be easily assembled even if a disk medium is small-sized.
Another object of the present invention is to provide a disk cartridge which enables easy recognition of the fact that the direction of insertion of a cartridge case, at the time of loading the disk cartridge into a disk drive device, is incorrect.
Still another object of the present invention is to provide a disk cartridge in which, at the time of loading the disk cartridge into a disk drive device, a shutter opening/closing member of the drive device can reliably engage with the one shutter member which is to be opened among the pair of shutter members which are provided correspondingly at the obverse and reverse surfaces of a recording disk.
Yet another object of the present invention is to provide a disk cartridge in which galling between a positioning pin and a reference hole does not arise at the time when a case is positioned in a drive device.
Still yet another object of the present invention is to provide a disk cartridge in which shells can be temporarily fastened together easily, the temporarily fastened state can be maintained, and the production loss can be reduced.
In a first aspect of the present invention, there is provided a disk cartridge comprising: a pair of case members having same configurations, and in a state in which the case members are superposed, the case members form a case in which a disk medium can be accommodated; opening portions provided in each of the case members, for access to the disk medium which is accommodated; a pair of shutter members provided at the pair of case members respectively, each shutter member movable, independently, between a closed position at which the shutter member closes a corresponding opening portion and an open position at which the shutter member opens the corresponding opening portion; a lock member provided for the shutter member, and able to lock the shutter member at the closed position; and an urging member provided for the shutter member, and able to urge the shutter member from the open position to the closed position, wherein at least one of the lock member and the urging member is provided in common for the pair of shutter members.
At the disk cartridge, the case is formed in the state in which the pair of case members are superposed together. The disk medium can be accommodated within the case.
An opening portion is formed in each of the case members. In the usual state, the shutter member is at the closed position. Further, the shutter member is locked at the closed position by the lock member. Thus, the opening portion is not inadvertently opened.
When locking of the shutter member by the lock member is released by the drive device or the like, the shutter member can move the open position. When, due to pressing of the shutter by the drive device or the like, the shutter member moves to the open position against the urging force of the urging member, the opening portion is opened. Thus, the drive device can access the disk medium, and can record or read information or the like. Note that a rotatable disk medium (i.e., a disk medium onto which information can be recorded or from which information can be read while the disk medium is being rotated) is usually used as the disk medium. In this case, for example, a spindle shaft or the like of the drive device is inserted in from the opening portion which has been opened, and can drive and rotate the disk medium.
An opening portion is provided at each of the case members. Thus, both surfaces of the disk medium can be accessed independently. The shutter members each independently move between the closed position and the open position. The lock member and the urging member as well lock and urge, respectively, each shutter member independently. Accordingly, at the time of opening or closing the opening portion of one case member, the opening portion of the other case member is not inadvertently opened or closed.
The case members forming the case have the same configuration. Thus, as compared with a case in which the case is structured by two or more case members having respectively different configurations, the number of parts can be reduced, and management of the number of parts is facilitated. For example, if the two case members are made to have symmetrical structures and one case member is inverted and superposed on the other case member, the case as well has a symmetrical structure. Thus, the disk cartridge can be used in an inverted state. Further, by making the case members have the same configuration, the case members can be manufactured by using a single molding device (e.g., a molding die), and management of precision is also facilitated.
In addition, the lock member and the urging member are provided in common for the shutter members. Namely, only one lock member and only one urging member are provided. Thus, as compared with a case in which a lock member and an urging member are provided for each shutter member, the number of parts can be reduced. The parts costs can thereby be reduced. Moreover, by reducing the number of parts, the assembly of the respective parts is also facilitated, and therefore, the assembly costs are also reduced.
In particular, even in cases in which the case members, the shutter members, the lock member and the urging member are made to be small-sized so as to correspond to a small-sized disk medium, these members can be assembled easily.
In a second aspect of the present invention, there is provided a disk cartridge accommodating a recording disk, as an information recording medium, within a cartridge case, and being inserted into a loading portion provided at a disk drive device, the disk cartridge comprising: a pair of shell members having same configurations, and being superposed together along a thickness direction of the recording disk so as to form the cartridge case; window portions formed in shell members so as to face an information recording surface at one side of the recording disk; shutter members provided at the shell members so as to be movable between a closed position, at which the shutter member closes the window portion, and an open position, at which the shutter member opens the window portion; guide grooves formed in the cartridge case at one side end surface corresponding to a direction of insertion of the cartridge case into the loading portion so as to extend, respectively, from both end portions of the one side end surface toward a center, and when the cartridge case is inserted into the loading portion so as to be oriented to a predetermined orientation (correct orientation), one portion of a shutter opening/closing member provided at the disk drive device is inserted into the guide groove and the guide groove guides the shutter opening/closing member to move along an opening/closing direction of the shutter member; and dummy grooves formed in the cartridge case at another side end surface at a side opposite to the one side end surface in which the guide grooves are formed, so as to extend, respectively, from both end portions of the other side end surface toward a center, and when the cartridge case is inserted into the loading portion so as to be oriented oppositely to the predetermined orientation (namely, wrong orientation), the one portion of the shutter opening/closing member is inserted into the dummy groove and the dummy groove guides the shutter opening/closing member to move along the opening/closing direction and restricts movement, to the open position, of the shutter opening/closing member.
In accordance with a disk cartridge of the second aspect of the present invention, dummy grooves are formed in the cartridge case at the other side end surface at the side opposite to the one side end surface in which the guide grooves are formed. Each dummy groove extends from an end portion of this other side end surface toward the center. In this way, when the cartridge case is inserted into the loading portion of the disk drive device so as to be oriented oppositely to the correct direction of insertion, a portion of the opening/closing member is inserted in the dummy groove, the shutter opening/closing member is guided by the dummy groove to move along the opening/closing direction of the shutter member, and movement of the shutter opening/closing member to the open position is restricted.
Accordingly, when the cartridge case is inserted into the loading portion of the disk drive device so as to be oriented oppositely, the shutter opening/closing member, which is in the midst of moving from the closed position to the open position, can no longer move. Thus, when it is detected that the shutter opening/closing member has stopped at the near side of the open position, it can be recognized that the cartridge case has been inserted into the loading portion of the disk drive device so as to be oriented oppositely to the correct direction. Further, it is possible to prevent the disk drive device and the disk cartridge from breaking due to one portion of the shutter opening/closing member colliding with the cartridge case or the like when the cartridge case is inserted into the loading portion of the disk drive device so as to be oriented oppositely.
Even if the disk cartridge is inserted into the loading portion of the disk drive device in the state in which the cartridge case is turned upside-down from the state at the time of the above-described insertion, the dummy grooves are formed in the cartridge case at the other side end surface at the side opposite to the one side end surface in which the guide grooves are formed, and extend from the both portions of this other side end surface toward the center. Thus, the shutter opening/closing member is reliably inserted into the dummy groove.
In accordance with a third aspect of the present invention, there is provided a disk cartridge accommodating a recording disk, as an information recording medium, within a cartridge case, and being removably loaded into a disk drive device, the disk cartridge comprising: a pair of shell members having same configurations, and being superposed together along a thickness direction of the recording disk so as to form the cartridge case; window portions formed respectively in the pair of shell members, each window portion facing a recording surface at one side of the recording disk; shutter members disposed at the pair of shell members, respectively, so as to be movable between a closed position, at which the shutter member closes the window portion, and an open position, at which the shutter member opens the window portion; shutter pushing portions, each projecting, in the thickness direction of the recording disk, from a shutter main body portion of the shutter member which moves in a region opposing the window portion, the shutter pushing portion being movable along a case front edge portion, which extends at the cartridge case substantially parallel to an opening/closing direction of the shutter members, while opposing the case front edge portion; and guide grooves provided in the case front edge portion so as to extend, respectively, from both widthwise direction end portions toward a central portion, and when the disk cartridge is loaded into the disk drive device, a shutter opening/closing member provided at the disk drive device enters into the guide groove and the guide groove guides the shutter opening/closing member to engage with the shutter pushing portion which corresponds to one recording surface of the recording disk at which recording surface information is to be recorded onto or played back from.
Accordingly, in accordance with the disk cartridge relating to the third aspect, even if the projecting length, by which the shutter pushing portion projects along the thickness direction of the recording disk from the shutter main body portion, cannot be made to be sufficiently long, if the groove width of the guide groove along the thickness direction is longer than the projecting length of the shutter pushing portion, the allowable range of the positional error, along the direction of thickness of the recording disk, of the shutter opening/closing member can be increased by an amount corresponding to the difference between the groove width of the guide groove and the projecting length of the shutter pushing portion. Thus, by setting the groove width of the guide groove in accordance with the actual positional error, along the thickness direction, of the shutter opening/closing member, the shutter opening/closing member can be guided so as to engage with the shutter pushing portion corresponding to the recording surface at the one side of the recording disk, at which recording surface information is to be recorded on or played back from.
In accordance with a fourth aspect of the present invention, there is provided a disk cartridge comprising: a case accommodating a disk medium whose both surfaces can be utilized by the case being inverted; (completely) circular reference holes (small diameter (size) holes) provided at both surfaces of the case, and due to the case being inverted, a positioning pin of a drive device is inserted into the circular reference hole and the circular reference hole carries out positioning of the case; and flat oval reference holes (large diameter (size) holes) provided at the both surfaces of the case, and due to the case being inverted, a positioning pin of the drive device is inserted into the flat oval reference hole and the flat oval reference hole, together with the circular reference hole, carries out positioning of the case, wherein a space is provided between the completely circular reference hole, which is formed from one surface of the case, and the flat oval reference hole, which is formed from another surface of the case and communicates with the completely circular reference hole, such that a distal end portion of the positioning pin does not interfere with the space when the case is positioned within the drive device.
In the fourth aspect of the present invention, a disk medium, whose both surfaces can be used by inverting a case, is accommodated within the case. A completely circular reference hole and a flat oval reference hole are provided in both surfaces of the case. By inverting the case, positioning pins of a drive device are inserted into the completely circular reference hole and the flat oval reference hole, and the case is positioned.
Here, positioning of the case is carried out by the completely circular reference hole and the flat oval reference hole. Positional offset between the completely circular reference hole and the positioning pin can be absorbed by making one of the reference holes be a flat oval reference hole. Thus, galling between the positioning pin and the completely circular reference hole can be mitigated.
The completely circular reference hole formed from one surface of the case and the flat oval reference hole formed from the other surface of the case communicate with one another. A space is provided between the completely circular reference hole and the flat oval reference hole, such that the distal end portion of the positioning pin does not interfere when the case is positioned within the drive device.
For example, in a case in which a space, which is such that the distal end portion of the positioning pin does not interfere when the case is positioned within the drive device, is not provided between the completely circular reference hole and the flat oval reference hole, there is the fear that the distal end portion of the positioning pin will pass through the flat oval reference hole formed from the other surface of the case and will fit-together with the completely circular reference hole.
By providing, between the completely circular reference hole and the flat oval reference hole, a space which is such that the distal end portion of the positioning pin does not interfere when the case is positioned within the drive device, even if the distal end portion of the positioning pin passes through the flat oval reference hole which is formed from the other surface of the case, due to the space which provided between the completely circular reference hole and the flat oval reference hole, the distal end portion of the positioning pin does not fit-together with the completely circular reference hole, and no galling arises between the distal end portion of the positioning pin and the completely circular reference hole.
An example of a method of providing a space, which is such that the distal end portion of the positioning pin does not interfere, between the completely circular reference hole and the flat oval reference hole, is a method in which the inner surface side of the case is made concave such that the peripheral portions of the completely circular reference hole and the flat oval reference hole are made to be thin. In this way, in the state in which the completely circular reference hole and the flat oval reference hole communicate with one another, a space is formed between the peripheral portion of the completely circular reference hole and the peripheral portion of the flat oval reference hole.
The depth of the space along the axial direction of the positioning pin (i.e., the distance by which the peripheral portion of the completely circular reference hole and the peripheral portion of the flat oval reference hole are separated from one another) is a depth such that the distal end portion of the positioning pin can be accommodated within the space when the case is positioned within the drive device. In this way, the distal end portion of the positioning pin does not pass through the flat oval reference hole formed from the other surface of the case, and does not interfere with the completely circular reference hole.
Other than the above-described method, an elongated hole, which communicates with the completely circular reference hole, may be provided in the inner surface side of the case. The depth of this elongated hole is a depth such that the distal end portion of the positioning pin can be accommodated within the elongated hole when the case is positioned within the drive device. In this way, even if the distal end portion of the positioning pin passes through the flat oval reference hole formed from the other surface of the case, it is positioned within the elongated hole. Thus, the distal end portion of the positioning pin does not reach the completely circular reference hole. Therefore, the distal end portion of the positioning pin does not fit-together with the completely circular reference hole.
In accordance with a fifth aspect of the present invention, there is provided a disk cartridge comprising: a pair of shells having same configurations, and in a state in which inner surface sides of the pair of shells are superposed, a disk medium is accommodated at an interior, and convex portions and concave portions, which can fit-together, are disposed at the pair of shells so as to oppose one another.
In the fifth aspect of the present invention, in a state in which inner surface sides of a pair of shells, which have the same configurations, are superposed, a disk medium is accommodated in the interior. Further, convex portions and concave portions, which can fit-together with one another in the state in which the inner surface sides of the shells are superposed, are disposed so as to oppose one another.
By fitting-together the convex portions and the concave portions which oppose one another, the pair of shells can be temporarily fastened. Thus, this temporarily fastened state can be maintained such that the shells do not separate from one another, up until the time that ultrasonic welding is carried out. Further, in the state in which the convex portions and the concave portions are fit-together, by making an adhesive or the like flow in so as to fix the shells, the two shells can be made integral in a state in which the positions of the shells are regulated. Thus, a highly-precise disk cartridge can be obtained.
The temporarily fastened state can be maintained in the state in which the convex portions and concave portions are fit-together. Thus, it is possible to, after various quality inspections have been carried out on the assembled (but not fixed) disk cartridge, ultimately fix only those disk cartridges which have passed inspection. If there is a disk cartridge which has not passed inspection, the disk cartridge can be disassembled merely by canceling the fit-together state of the convex portions and the concave portions. Thus, those parts which can be reused can be utilized again, and the production loss can be reduced.
The shells can be fixed together by making the concave portions be through-holes, and by melting and deforming the distal end portions of the convex portions exposed at the outer surface side of the shell. In this way, the shells can be fixed together, not just by adhesion, but by ultrasonic welding as well. Further, in this case, it suffices to deform only the distal end portions of the convex portions. Thus, it is possible to use less vibration energy which is applied by the ultrasonic welding, the generation of dust can be suppressed, and there are few effects on the disk cartridge.
The through hole can be made to be a stepped structure formed by a fit-together portion, which is provided at the inner surface side of the shell and which fits-together with the convex portion, and a large diameter portion, which is provided at the outer surface side of the shell and whose diameter is larger than that of the fit-together portion. In this way, the deformed distal end portion of the convex portion is accommodated in the large diameter portion. Therefore, the convex portion is prevented from being pulled out, and the fixing strength can be ensured. Moreover, the distal end portion of the convex portion which has been melted does not project out from the outer surface side of the shell. Here, providing a taper, whose diameter increases from the inner surface side of the shell toward the outer surface side, at the large diameter portion is even more effective.
By fixing the shells together, there is the fear that, due to the vibration energy applied due to the ultrasonic welding, excessive stress will be applied to the base portion of the convex portion, and the base portion may break or the like. However, by providing an R portion or a C surface portion at the base end side of the convex portion, the convex portion is reinforced and is made difficult to break.
In accordance with a sixth aspect of the present invention according to the first aspect, the lock member is provided in common for the pair of the shutter members, and able to lock each of the shutter members independently at the closed position; and the urging member is provided in common for the pair of shutter members, and able to urge each of the shutter members independently from the open position to the closed position.
In accordance with a seventh aspect of the present invention according to the first aspect, the lock member has rotation symmetry configuration with respect to a symmetry axis of the disk cartridge, which is parallel to an inserting direction of the disk cartridge.
In accordance with an eighth aspect of the present invention according to the first aspect, the urging member has rotation symmetry configuration with respect to a symmetry axis of the disk cartridge, which is parallel to an inserting direction of the disk cartridge.
In accordance with a ninth aspect of the present invention according to the second aspect, the dummy groove includes a stopper, and the dummy groove restricts the movement, to the open position, of the shutter opening/closing member by the shutter opening/closing member being abutted to the stopper.
In accordance with a tenth aspect of the present invention according to the ninth aspect, a pressed portion, which is pressed by the shutter opening/closing member, is provided in the shutter member, and the stopper is positioned, in a cartridge case-widthwise direction orthogonal to an inserting direction of the cartridge case, outside the pressed portion of the shutter member positioned in the open position.
In accordance with an eleventh aspect of the present invention according to the third aspect, the guide groove is formed such that a width in the thickness direction at an outside end portion, in the widthwise direction, of the guide groove is larger than that at a center side end portion of the guide groove.
In accordance with a twelfth aspect of the present invention according to the third aspect, a length, in the thickness direction, of a portion of the shutter pushing portion is smaller than a width, in the thickness direction, of a groove formed in the case front edge portion, the portion of the shutter pushing portion facing the groove.
In accordance with a thirteenth aspect of the present invention according to the third aspect, an outside end portion, in the widthwise direction, of the shutter pushing portion is inclined with respect to the thickness direction.
In accordance with a fourteenth aspect of the present invention according to the fourth aspect, the flat oval reference hole includes the space, and a dimension, in a thickness direction of the disk medium, of the flat oval reference hole is set such that a tip end of the positioning pin is accommodated within the flat oval reference hole when insertion of the positioning pin.
In accordance with a fifteenth aspect of the present invention according to the fourth aspect, a dimension, in a thickness direction of the disk medium, of the space is set such that a tip end of the positioning pin is accommodated within the space when insertion of the positioning pin.
In accordance with a sixteenth aspect of the present invention according to the fifth aspect, the concave portion is a penetration hole and the convex portion is inserted into the penetration hole.
In accordance with a seventeenth aspect of the present invention according to the sixteenth aspect, the penetration hole comprises a small dimension portion for engaging the convex portion and a large diameter portion larger than the small dimension portion.